ANSYS Coupled-Field Analysis Guide phần 3 ppsx

It provides you with the ability tosolve coupled-field problems such as the following: • Joule Heating thermal/electric/structural coupling • Fluid Solid Interaction Analysis fluid/struc

autos,on ! auto time-stepping

deltim,1e-5,1e-6,delt,on ! time step control

outres,basic,all ! save all load step information

physics,write,thermal ! write thermal physics file

finish

*do,i,1,ftime/tinc ! solution *do loop

time=time+tinc ! increment time

physics,read,emag ! read emag physics file

physics,read,thermal ! read thermal physics file

/assign,esav,therm,esav ! redirect files for use in thermal restart

time,time ! time at end of thermal run

esel,s,mat,,2 ! select billet region

ldread,hgen,,,,2,,rmg ! apply coupled joule heating load from emag

save ! save database

/post26 ! time-history postprocessor

/show

nsol,2,1,temp,,tempcl ! store temperature at billet centerline

nsol,3,2,temp,,tempsurf ! store temperature at billet outer diameter

plvar,2,3 ! plot temperature rise over time

prvar,2,3 ! print temperature rise over time

finish

2.8.2.10 Results

Figure 2.18: “Temperature Response of Solid Cylinder Billet” shows the temperature results obtained in thisanalysis

Figure 2.18 Temperature Response of Solid Cylinder Billet

MFS Single-Code Coupling

This chapter describes the ANSYS Multi-field solver- single code (MFS), available for a large class of coupledanalysis problems An automated tool for solving sequentially coupled field problems, the ANSYS Multi-fieldsolversupersedes the physics file-based procedure and provides a robust, accurate, and easy to use tool forsolving sequentially coupled physics problems It is built on the premise that each physics is created as a fieldwith an independent solid model and mesh You can identify surfaces or volumes for coupled load transfer, andthen use a set of multi-field solver commands to configure the problem and define the solution sequencing Thesolver automatically transfers coupled loads across dissimilar meshes The MFS solver is applicable to static,harmonic, and transient analysis, depending on the physics requirements Any number of fields can be solved

in a sequential (staggered) manner

The ANSYS Multi-field solver is one of two versions of the multi-field solver (see Chapter 4, “Multi-field AnalysisUsing Code Coupling” for a description of the other version, the MFX solver) The MFS solver is the basic multi-field solver used if the simulation involves small models that have all physics field contained within a singleprogram (e.g., ANSYS) The MFS solver uses iterative coupling where each physics is solved sequentially and eachmatrix equation solved separately The solver iterates between each physics field until the loads transferredacross physics interfaces converge

The ANSYS Multi-field solver has the following main features:

• Each physics is created as a "field" with an independent model and mesh

• Each field is defined by a group of element types

• Load transfer regions are identified by surfaces and/or volumes

• Each field may have different analysis types

• Each field may have different solvers and analysis options

• Each field may have a different mesh discretization

• Surface load transfer can occur across fields

• Volumetric load transfer can occur across fields

• Independent results files are created for each field

The ANSYS Multi-field solver can solve a large class of coupled field problems Typical applications include thefollowing:

• Current conduction-magnetostatics

The following ANSYS Multi-field solver (MFS) topics are available:

3.1 The ANSYS Multi-field solver and Solution Algorithm

3.2 ANSYS Multi-field solver Solution Procedure

3.3 Sample Thermal-Stress Analysis of a Thick-walled Cylinder (Batch or Command Method)

3.4 Sample Electrostatic Actuated Beam Analysis (Batch or Command Method)

3.5 Sample Induction-Heating Analysis of a Circular Billet

3.1 The ANSYS Multi-field solver and Solution Algorithm

The ANSYS Multi-field solver is available in the ANSYS Multiphysics product It provides you with the ability tosolve coupled-field problems such as the following:

• Joule Heating (thermal/electric/structural coupling)

• Fluid Solid Interaction Analysis (fluid/structural coupling)

The following ANSYS Multi-field solver algorithm topics are available:

The ANSYS Multi-field solver automatically transfers coupled loads across dissimilar meshes Two interpolationmethods are available for a load transfer: profile preserving and globally conservative In a profile preservinginterpolation, each node on the receiver side maps onto an element on the sender side (αi) The transfer variable

is then interpolated at αi The transfer value is Ti = φ (αi) Thus, all nodes on the receiver side query the senderside

Figure 3.1 Profile Preserving Interpolation

Figure 3.2 Globally Conservative Interpolation

Some important points to remember about the interpolation methods are:

• For a profile preserving interpolation, the forces and heat rate will not balance on this interface For aglobally conservative interpolation, total force and total heat rate will balance on this interface However,locally the distributions might not agree

Figure 3.3 Profile Preserving Interpolation - Load Imbalances





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• As shown in the following figures, for a profile preserving interpolation, you should have a coarse mesh

on the sending side and a fine mesh on the receiver side, rather than the converse When the coarse mesh

is on the sending side, the receiver adequately captures the normal heat flux profile On the receiver side,

a fine mesh ensures a sufficient number of nodes When the coarse mesh is on the receiver side, the ceiver does not adequately capture the normal heat flux profile due to an insufficient number of nodes

re-on the receiver side

Figure 3.5 Profile Preserving Interpolation - Coarse Mesh on the Sending Side

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• As shown in the following figures, for a globally conservative interpolation it is better to have a fine mesh

on the sending side and a coarse mesh on the receiver side than the converse When the fine mesh is onthe sending side, the receiver adequately captures the forces When the fine mesh is on the receiver side,the load distribution on the receiver might not be captured, even though the total force on the receiver

is equal to the total force on the sender

Figure 3.7 Globally Conservative Interpolation - Fine Mesh on Sending Side

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• The above two points hold true if either the sender or receiver mesh is made of higher order elements.Exercise care if you wish to produce a node-to-node mapping from higher order elements to lower orderelements For example, as shown in the following figure, a globally conservative load transfer across aninterface that has the same number of elements on both sides will not produce the correct profile if thereceiver is higher order

Figure 3.9 Three Lower Order Elements

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Figure 3.10 Six Lower Order Elements

Figure 3.11 Fluid-Solid Interaction Load Transfer

between the two meshes The element that minimizes the distance is then selected In the following figure, node

N1 is found in elements e1 and e2, so it is mapped to the element which minimizes the gap distance (e1 because

The global method has a complexity of θ(n x m) where n is the number of nodes mapped onto m elements If n

and m are of the same order, the time required to compute the mapping grows quadratically and leads to putational inefficiency, especially for large models

com-Note — The same issues exist for 3-D models involving surface-to-surface mapping They are also

en-countered for volumetric mapping in 2-D and 3-D models

Bucket Search Method

The bucket search method is designed to alleviate the inefficiency problem that the global method has whenthe number of nodes increases The underlying ideas for the bucket search method are presented in the book

Computational Nonlinear Mechanics in Aerospace Engineering, American Institute of Aeronautics and Astronautics, edited by S Atluri, ISBN 1563470446, Chapter 5, Fast Projection Algorithm for Unstructured Meshes by K Jansen,

F Shakib, and T Hughes, 1992

For a given node, the bucket search method restricts the elements over which it loops This is accomplished asfollows:

2 The node in question is then located in a box.

3 The global method is used for the node in question, but the elements are restricted to that box only.For example, in the following figure, elements e1, e2, and e3 are in box 1, elements e3 and e4 are in box 2, and e4,

e5, and e6 are in box 3 Node N1 searches only over the elements in box 3

Figure 3.14 Node in Box 3 with Three Elements

When the node in question is in a box with elements, the mapping is identical to global mapping

While this procedure appears straightforward, it is more complex when the node in question is in an empty box

as shown in the following figure This can occur when there are gap/penetration issues or the interface edgesare misaligned

Figure 3.15 Nine boxes and Node in Empty Box

Note — This same mapping process is used for 3-D models involving surface-to-surface mapping and

2-D and 3-2-D models involving volumetric mapping

3.1.2.2 Mapping Diagnostics

You can use the MFTOL command (Main Menu> Preprocessor> Multi-field Set Up> MFS-Single Code>

Setup> Global) to turn normal distance checking on for surface mapping and to set a normal distance limit from

a node to an element surface The normal distance limit defaults to 1.0e-6

As shown in the following figure, in surface mapping, improperly mapped nodes include nodes that exceed thenormal distance limit specified (figure a) and nodes that are on misaligned surfaces (figure b) In volumetricmapping, improperly mapped nodes are nodes out of the target domain (figure c).

Figure 3.16 Improperly Mapped Nodes

The mapping tool creates components to graphically display nodes that are improperly mapped Component

number_label_field number (for example, MFVO_2_1_HGEN_2)

3.1.2.3 Mapping Operations

You can use the MFMAP command (Main Menu> Preprocessor> Multi-field Set Up> MFS-Single Code>

In-terface> Mapping) to calculate, save, resume, or delete mapping data By saving mapping data to a file and

using resume, you might be able to significantly reduce computing time during a restart or another solve If youwish to resume a mapping file, be sure to first delete any existing mapping data in memory You can also use

this command to check your mapping without performing a solution See the ANSYS Commands Reference for

more information about this command

3.1.3 Coupled Field Loads

The following tables show the loads that the ANSYS Multi-field solver can transfer in a coupled physics analysis

Table 3.1 Load Transfer Between Fields

Fluid Magnetic

Electric Thermal

Structural Field

4 3

2 1

Structural

7 6

Thermal Structural

Volumetric Load Transfer

Temperature Displacements

Send

Displacements Temperature

Receive

2 Electrostatic - Structural Coupling

Electrostatic Structural

Surface Load Transfer

Forces Displacements

Send

Displacements Forces

Receive

3 Structural - Magnetic Coupling

Magnetic Structural

Surface or Volumetric Load

Transfer

Forces Displacements

Send

Displacements Forces

Receive

4 Structural - Fluid Coupling

Fluid Structural

Surface Load Transfer

Forces Displacements

Send

Displacements Forces

Receive

5 Thermal - Electric Coupling

Electric Thermal

Volumetric Load Transfer

Heat Generation Temperature

Send

Temperature Heat Generation

Receive

6 Thermal - Magnetic Coupling

Magnetic Thermal

Volumetric Load Transfer

Heat Generation Temperature

Send

Temperature Heat Generation

Receive

7 Thermal - Fluid Coupling

Fluid Thermal

Surface Load Transfer

Temperature/Heat Flux Temperature/Heat Flux

Send

Heat Flux/Temperature Heat Flux/Temperature

Receive

8 Magnetic - Fluid Coupling

Fluid Magnetic

Volumetric Load Transfer

— Forces

Send

Forces

—

Receive

3.1.4 Elements Supported

The ANSYS Multi-field solver supports the elements shown in the following tables These elements support the

SF family of commands (SF, SFA, SFE, or SFL) for surface load transfer (field surface interface: FSIN flag) and the

BFE command for volumetric load transfer (field volume interface: FVIN flag) during an analysis You need to

flag these elements at the surface (FSIN) and volume (FVIN) interface for load transfer to other fields during theanalysis Other elements types can be used in any of the field analyses, but they will not participate in loadtransfer

Table 3.2 Structural and Thermal Elements

Structural Elements

SHELL BEAM

SOLID PLANE

SHELL51 BEAM3

SOLID45 PLANE2

SHELL63 BEAM23

SOLID92 PLANE42

SHELL93 BEAM188

SOLID95 PLANE82

SHELL181 BEAM189

SOLID185 PLANE182

SOLSH190 SOLID186

PLANE183

SOLID187

Thermal Elements

SHELL SOLID

PLANE

SHELL57 SOLID70

PLANE35

SOLID87 PLANE55

SOLID90 PLANE77

Table 3.3 Electromagnetic, Fluid, and Coupled-Field Elements

Electromagnetic Elements

HF SOLID

PLANE

HF119 SOLID96

PLANE53

HF120 SOLID97

PLANE121

SOLID117 PLANE230

SOLID122 SOLID123 SOLID231 SOLID232

Fluid Elements SOLID

PLANE

SHELL157 SOLID5

PLANE13

Electromagnetic Elements

SOLID98 PLANE226 PLANE227

1 You can use the FLOTRAN remeshing capability in a fluid-solid interaction analysis See Section 7.3:

Remeshing in the ANSYS Fluids Analysis Guide for additional information.

3.1.5 Solution Algorithm

The solution algorithm for the ANSYS Multi-field solver is shown in the following figure The MFANALYSIS

command activates a solution The solution loop consists of three loops: field loop, stagger loop, and time loop.The ANSYS Multi-field solver supports transient, static, and harmonic analysis of fields inside the field loop

Figure 3.17 ANSYS Multi-field solver Algorithm

Within each time loop is the stagger loop The stagger loop allows for implicit coupling of the fields in the MFSsolution Within each step in the time loop, the field solutions are repeated in the stagger loop until convergence.The number of iterations within the stagger loop is determined by the convergence of the loads transfer between

fields or the maximum number of stagger iterations specified by the MFITER command.

Within each stagger loop is the field loop The field loop contains the analysis of each field solution The fieldLoop is set up like any single ANSYS analysis Each field can be set up by grouping a set of element types using

the MFELEM command Solution options for each field are set using the MFCMMAND command Surface and volumetric load transfer between fields is specified using the MFSURFACE and MFVOLUME commands, respect-

ively Fields can share a dissimilar mesh across the interface and load transfer from a field occurs after the solution

of the respective field Load transfer to a particular field occurs before solution of the field Morphing (MORPH

command) of a non-structural field mesh occurs prior to the field solution The morphing is based on displacements

of a previous structural field solution

Remeshing in the ANSYS Fluids Analysis Guide for additional information.

3. 1.5 Solution Algorithm

The... See the ANSYS Commands Reference for

more information about this command

3. 1 .3 Coupled Field Loads

The following tables show the loads that the ANSYS Multi-field...

PLANE35

SOLID87 PLANE55

SOLID90 PLANE77

Table 3. 3 Electromagnetic, Fluid, and Coupled-Field Elements

Electromagnetic